Method and apparatus for transmitting information about available power of terminal in mobile communication system

ABSTRACT

A method for transmitting power headroom information by a terminal in a mobile communication system, in which power headroom information is generated and transmitted if a change in power headroom is greater than or equal to a predetermined threshold and a total amount of data stored in a buffer of the terminal is greater than or equal to an other predetermined threshold.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to KoreanPatent Application Serial Nos. 10-2008-0003669 and 10-2008-0060513,filed in the Korean Intellectual Property Office on Jan. 11, 2008 andJun. 25, 2008, respectively, and to PCT/KR2009/000091, filed Jan. 8,2009, the contents of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method and apparatus fortransmitting information needed to allocate transmission resources toUser Equipment (UE) in a mobile communication system and, moreparticularly, to a method and apparatus for transmitting power headroominformation of UEs in a mobile communication system.

2. Description of the Related Art

A Universal Mobile Telecommunication Service (UMTS) system is a 3^(rd)generation asynchronous mobile communication system that uses WidebandCode Division Multiple Access (WCDMA) based on Global System for Mobilecommunication (GSM) and General Packet Radio Services (GPRS), which areEuropean mobile communication systems.

The 3^(rd) Generation Partnership Project (3GPP), now in charge of UMTSstandardization, considers Long Term Evolution (LTE) to be thenext-generation mobile communication system of the UMTS system. LTE, atechnology for implementing high-speed packet-based communication at atransfer rate reaching approximately 100 Mbps, is expected to becommercialized in about 2010. To this end, several schemes have beendiscussed, including a scheme to reduce the number of nodes located incommunication paths by simplifying the network structure, and a schemeto align wireless protocols and wireless channels, as closely aspossible.

Referring to FIG. 1, Evolved Radio Access Networks (E-RANs) 110 and 112are simplified to 2-node structures consisting of Evolved Node Bs (ENBs)120, 122, 124, 126 and 128, and Enhanced Gateway GPRS Support Nodes(EGGSN) 130 and 132. A User Equipment (UE) 101 accesses an InternetProtocol (IP) network 114 by way of the E-RANs 110 and 112.

The ENBs 120, 122, 124, 126 and 128 correspond to the legacy Node Bs ofthe UMTS system, and are connected to the UE 101 by wireless channels.Compared with the legacy Node Bs, the ENBs 120, 122, 124, 126 and 128perform more complex functions.

In the next-generation mobile communication system (hereinafter referredto as “LTE”), since all user traffic including real-time services suchas Voice over IP (VoIP) is serviced through a shared channel, a devicefor performing scheduling by collecting status information of UEs isneeded, and the ENBs 120, 122, 124, 126 and 128 are responsible for thescheduling. To implement the transfer rate of up to 100 Mbps, LTE usesOrthogonal Frequency Division Multiplexing (OFDM) as a wireless accesstechnology in a bandwidth of up to 20 MHz. In addition, AdaptiveModulation & Coding (AMC) for determining a modulation scheme and achannel coding rate according to the channel status of the UE isapplied.

An ENB (“base station”) receives reports on information received fromthe UEs (“terminals”) to perform an operation of allocating transmissionresources to the terminals, i.e., to perform scheduling, and an exampleof such information may include Buffer Status Report (BSR) indicatinginformation about the amount and type of data stored in the terminals,and information about power headroom of the terminals.

The BSR provides information indicating the amount of data stored in aterminal according to priority, and this information is generated andtransmitted by the terminal to the base station if particular conditionsare satisfied. The particular conditions may include, for example, asituation in which new data has occurred in a terminal that stores nodata, and a situation in which a predetermined time has elapsed aftertransmission of BSR.

The power headroom information indicates the maximum available powerthat the terminal can use for uplink data transmission, given thecurrent channel condition of the UE.

Although the size of the power headroom information is only a few bytes,1 Resource Block (RB) which is the minimum transmission resource unitshould be used to transmit the power headroom information, in view ofcharacteristics of the OFDM communication system. Therefore, given thata total of 25 RBs exist in a system with a 5-MHz bandwidth, it isnecessary to reduce the frequency of transmission of the power headroominformation by generating and transmitting the power headroominformation only when absolutely necessary.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems, and the present invention provides a methodand an apparatus for efficiently transmitting and receiving controlinformation for receiving a service in a broadcast communication system.

An aspect of the present invention is to provide a power headroominformation transmission method and apparatus for reducing the frequencyof transmission of power headroom information of a terminal in a mobilecommunication system.

Another aspect of the present invention is to provide a method andapparatus to more efficiently use uplink transmission resources byreducing the frequency of transmission of power headroom information ofa terminal in a mobile communication system.

In accordance with one aspect of the present invention, there isprovided a method for transmitting power headroom information by aterminal in a mobile communication system. The method includesgenerating and transmitting power headroom information if a change inpower headroom is greater than or equal to a predetermined threshold anda total amount of data stored in a buffer of the terminal is greaterthan or equal to a predetermined threshold.

In accordance with another aspect of the present invention, there isprovided a method for transmitting power headroom information by aterminal in a mobile communication system. The method includes measuringa change in power headroom, determining whether the measured change inpower headroom satisfies a first condition, determining whether a totalamount of data stored in a buffer of the terminal satisfies a secondcondition, generating the power headroom information if the first andsecond conditions are satisfied, and transmitting uplink data includingthe generated power headroom information.

In accordance with a further another aspect of the present invention,there is provided a terminal apparatus for transmitting power headroominformation in a mobile communication system. The terminal apparatusincludes a controller for measuring a change in power headroom, andgenerating power headroom information if the measured change in powerheadroom is greater than or equal to a predetermined threshold and atotal amount of data stored in a buffer of the terminal is greater thanor equal to a predetermined threshold, and a multiplexer formultiplexing uplink data with the generated power headroom information.

In accordance with yet another aspect of the present invention, there isprovided a terminal apparatus for transmitting power headroominformation in a mobile communication system. The terminal apparatusincludes a transceiver for measuring a change in power headroom, acontroller for comparing the measured change in power headroom with afirst condition, comparing a total amount of data stored in a bufferwith a second condition, and generating the power headroom informationif the first and second conditions are satisfied, and a multiplexer formultiplexing uplink data received from an upper layer device with thegenerated power headroom information.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 provides an example of architecture of the next-generation mobilecommunication system based on the UMTS system;

FIG. 2 is a flowchart showing an example of a method for determining thesatisfaction/non-satisfaction of a first condition (Condition 1) fortransmission of power headroom information in a terminal according to anembodiment of the present invention;

FIG. 3 is a flowchart showing a method for transmitting power headroominformation in a terminal according to a first embodiment of the presentinvention;

FIG. 4 is a flowchart showing a method for transmitting power headroominformation in a terminal according to a second embodiment of thepresent invention;

FIG. 5 is a flowchart showing a method for transmitting power headroominformation in a terminal according to a third embodiment of the presentinvention; and

FIG. 6 is a block diagram of a terminal for transmitting power headroominformation according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings. It should be notedthat throughout the drawings, the same drawing reference numerals willbe understood to refer to the same elements, features and structures. Inthe following description, specific details such as detailedconfiguration and components are merely provided to assist the overallunderstanding of exemplary embodiments of the present invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

In the following description, embodiments of the present invention willbe presented to accomplish the foregoing technical objectives. Althoughthe same names of entities as those defined in 3^(rd) GenerationPartnership Project (3GPP), which is the asynchronous mobilecommunication standard, or in Long Term Evolution (LTE), which is thenext-generation mobile communication system currently being discussed ofthe UMTS system will be used for the convenience of a description of thepresent invention, the scope of the present invention will not belimited to such standards and names, and the invention may be applied toany systems with the similar technical background.

The necessary amount of power headroom information of terminalsincreases when a scheduler of a base station aggressively allocatestransmission resources to the terminals. In other words, the utility ofpower headroom information of terminals increases when the base stationintends to allocate many transmission resources to the terminals, butlittle power headroom information is needed when the base stationallocates less transmission resources to the terminals. To describe thisin more detail, a brief description is provided below of a definition ofthe power headroom and a method of setting uplink transmission output bya terminal during uplink data transmission.

Power headroom of a terminal is commonly calculated by Equation (1):Power Headroom=10 log₁₀(P _(MAX))−10 log₁₀(P _(tx) _(—) _(lowest) _(—)_(mcs))  (1)where P_(MAX) is the maximum transmission output of the terminal, andP_(tx) _(—) _(lowest) _(—) _(mcs) is the transmission output requiredwhen the terminal transmits data with one Resource Block (RS) byapplying the lowest Modulation Coding Scheme (MCS) level. The P_(MAX)may be determined depending on the device characteristics of theterminal or may be designated for respective terminals on an individualbasis by the base station in a call setup process.

When an arbitrary MCS level is applied and data is transmitted with nnumber of RBs, required transmission power P_(REQUIRED) is calculated byEquation (2):P _(REQUIRED)=10 log n+Po+α×PL+delta_(—) mcs+f(delta_(—) i)  (2)where Po and α are positive real numbers that are stored in the terminalor signaled by the base station in a call setup process, PL is a pathloss measured by the terminal, delta_mcs is an arbitrary integer thathas been predetermined for each MCS level individually, and f(delta_i)is a value that the terminal obtains by inputting uplink transmissionoutput control commands received up to now, to a specific function f( ).

The transmission output the terminal actually uses is limited by theP_(MAX). Namely, the actual transmission output P of the terminal iscalculated by Equation (3):P=min(P _(MAX) ,P _(REQUIRED))  (3)

Upon receiving a scheduling command to transmit data with apredetermined number of RBs at an arbitrary time by applying anarbitrary MCS level, the terminal calculates P_(REQUIRED) using Equation(2). Thereafter, using Equation (3), the terminal transmits data withthe P_(REQUIRED) if the calculated P_(REQUIRED) does not exceed theP_(MAX), and the terminal transmits data with the P_(MAX) if thecalculated P_(REQUIRED) exceeds the P_(MAX). Since the P_(REQUIRED)exceeding the P_(MAX) indicates an impossibility of applying therequired transmission output, the scheduler should allocate transmissionresources and apply an MCS level to the terminal so that this situationdoes not occur.

The power headroom of the terminal is information that the base stationreferences to perform scheduling such that P_(REQUIRED) does not exceedP_(MAX), when allocating transmission resources and applying an MCSlevel to the terminal.

As shown in Equation (1), since the power headroom is determined byP_(tx) _(—) _(lowest) _(—) _(mcs), and P_(tx) _(—) _(lowest) _(—) _(mcs)is P_(REQUIRED) when applying the lowest MCS level and transmitting datawith one RB, factors used for determining the power headroom include Po,α, PL and f(delta_i). Since Po and α are constants and the uplinktransmission output control commands are generated by the base station,f(delta_i) is also a value know to the base station. Meanwhile, sincethe path loss is measured by the terminal, it is a variable unknown tothe base station, and if the power headroom of the terminal changes dueto the abrupt change in the path loss, the base station may notrecognize the change.

Therefore, if the path loss abruptly changes, the changed power headroomneeds to be reported to the base station. However, even though the pathloss of the terminal suddenly changes or the power headroom abruptlychanges accordingly, it is inefficient to always report new powerheadroom to the base station.

As described above, the power headroom information of the terminal isneeded when P_(REQUIRED) is likely to exceed P_(MAX) as the base stationallocates many transmission resources and applies a high MCS level, tothe terminal. However, if the amount of data stored in the terminal isnegligible, there is a low possibility that many transmission resourceswill be allocated to the terminal and a high MCS level will be appliedto the terminal.

In an embodiment of the present invention that addresses the abovescenario, the terminal generates and transmits power headroominformation using the following two conditions:

Condition 1 A change in path loss exceeds Δ.

Condition 2 The amount of data stored in a terminal exceeds a dataamount threshold (“Y”).

In Condition 1, a change in power headroom or a change in ChannelQuality Information (CQI) may be used instead of the change in pathloss.

In Condition 1, a terminal may determine the change in power headroom byclassifying power headrooms indicated by code points according to areas,and then applying different thresholds to the respective areas. Thereason why the terminal uses the above method is as follows. If thepower headroom is large, there is a low possibility that the basestation will perform scheduling so that P_(REQUIRED) exceeds P_(MAX),since the changed power headroom still has a large value despite thesignificant change. However, if the power headroom is small, there is ahigh possibility that the base station will perform scheduling so thatP_(REQUIRED) exceeds P_(MAX) despite an insignificant change in powerheadroom.

In the following description, it is assumed that the power headroominformation consists of 8 bits and the power headroom indicated by eachcode point of the power headroom information is as shown in Table 1.

TABLE 1 Power Headroom Information Power Headroom Area  0 X₀ Area 1 . .. . . . . . . N − 1 X_((N−1)) Area 1 N X_(N) Area 2 . . . . . . . . . M− 1 X_((M−1)) Area 2 M X_(M) Area 3 . . . . . . . . . 255 X₂₅₅ Area 3

Referring to Table 1, the area between power headrooms X₀ and X_((N-1))is defined as an area 1, the area between power headrooms X_(N) andX_((M-1)) as an area 2, and the area between power headrooms X_((M-1))and X₂₅₅ as an area 3.

Based on Table 1, if the last reported power headroom belongs to thearea 1, a terminal according to an embodiment of the present inventiondetermines that the power headroom has changed by a predeterminedthreshold or more, only when a difference between the current powerheadroom and the last reported power headroom is greater than or equalto Δ₁. If the last reported power headroom belongs to the area 2, theterminal determines that the power headroom has changed by apredetermined threshold or more, only when a difference between thecurrent power headroom and the last reported power headroom is greaterthan or equal to Δ₂. If the last reported power headroom belongs to thearea 3, the terminal determines that the power headroom has changed by apredetermined threshold or more, only when a difference between thecurrent power headroom and the last reported power headroom is greaterthan or equal to Δ₃.

Namely, if the satisfaction/non-satisfaction of Condition 1 isdetermined depending on the change in power headroom, the terminaloperates as specified in FIG. 2.

Referring to FIG. 2, in step 205, the terminal recognizes power headroominformation, a power headroom area, and an area-specific changethreshold through a call setup process. Recognizing power headroominformation by the terminal in step 205 refers to recognizing a mappingrelationship between code points of power headroom information and powerheadrooms. Recognizing a power headroom area by the terminal in step 205refers to recognizing an area to which the power headroom belongs, forexample, recognizing a certain area to which an arbitrary power headroombelongs, regarding all power headrooms between the power headroom mappedto the minimum value of the power headroom information and the powerheadroom mapped to the minimum value. Recognizing an area-specificchange threshold by the terminal in step 205 refers to, if n powerheadroom areas have been defined, recognizing change thresholds Δ1, Δ2,. . . , Δn, defined for their associated n power headroom areas.

In step 210, the terminal generates and transmits power headroominformation while performing the common uplink data transmissionprocess. After successfully transmitting the power headroom information,the terminal checks an area to which the reported power headroombelongs, in the power headroom information in step 215. Here, thereported power headroom's area is defined as k.

In step 220, the terminal continuously measures the power headroom. Instep 225, the terminal calculates a difference between the measuredcurrent power headroom and the reported power headroom, and checks ifthe difference is greater than a change threshold Δk of the area k. Ifthe difference between the measured current power headroom and thereported power headroom is greater than the threshold Δk in step 225,the terminal determines in step 230 that Condition 1 is satisfied. Ifthe terminal determines in step 230 that Condition 1 is satisfied, theterminal returns to step 220 and continues a necessary operation ofgenerating the power headroom information, or may end the operationdepending on the situation.

However, if the difference between the measured current power headroomand the reported power headroom is less than or equal to the thresholdΔk in step 225, the terminal determines in step 235 that Condition 1 isunsatisfied. Having determined the non-satisfaction of Condition 1 instep 225, the terminal returns from step 235 to step 220 and continuesto measure power headroom. In step 235, the terminal may terminate theoperation depending on the situation.

The reason why the terminal uses Condition 2 in determining whether togenerate power headroom information is as follows. If the amount of datastored in the terminal is small, the utility of the power headroominformation also falls. Thus, the terminal need not generate andtransmit the power headroom information if the amount of stored data isless than or equal to a predetermined threshold. As an extreme example,if the terminal has no data to transmit, utility value of the powerheadroom information does not exist. There is a property that the dataamount threshold Y of Condition 2 is in inverse proportion to thefrequency of occurrence of power headroom information. That is, as Yincreases, the frequency of occurrence of power headroom information isreduced, and as Y is lower, the frequency of occurrence of powerheadroom information increases. The network may set a different valuefor Y according to the terminal characteristics or the cell conditions.For example, since it is likely that more transmission resources will beallocated to a terminal used by a premium user, a low data amountthreshold Y may be set to the terminal so that power headroominformation may be generated more frequently. On the other hand, in ahigh-cell load environment in which there is a low possibility that moretransmission resources will be allocated to an arbitrary terminal, thefrequency of occurrence of power headroom information may be reduced byincreasing the data amount threshold Y.

Now, a description will be made of first to third embodiments of thepresent invention for generating and transmitting power headroominformation using Condition 1 and Condition 2 described above.

First Embodiment

Referring to FIG. 3, the terminal recognizes Condition 1 and Condition2, which are power headroom information generation conditions, in step305. Condition 1, as described above, is satisfied when a change in pathloss is greater than or equal to a predetermined threshold, when achange in power headroom is greater than or equal to a predeterminedarea-specific threshold, or when a change in CQI is greater than orequal to a predetermined threshold.

In step 310, the terminal starts an uplink data transmission processaccording to a predetermined procedure. In step 315, the terminalmeasures its power headroom while performing uplink data transmission.That is, the terminal receives uplink scheduling information through adownlink control channel, and measures its path loss, power headroom, ordownlink channel quality at intervals of a predetermined period, whiletransmitting uplink data according to the received schedulinginformation. The uplink scheduling information is information thatindicates allocated transmission resources and an MCS level to beapplied.

In step 320, the terminal determines whether Condition 1 is satisfied.That is, the terminal determines whether a difference between thecurrent path loss measured at stated intervals and a path loss used tocalculate power headroom of the power headroom information that has beenlast transmitted successfully exceeds a predetermined thresholdindicated in Condition 1. The terminal may also determine whether adifference between the current power headroom measured at statedintervals and the power headroom that has been last reportedsuccessfully exceeds a predetermined threshold indicated in Condition 1.The predetermined threshold indicated in Condition 1 may be differentlydefined according to the area, and a threshold corresponding to an areato which the power headroom belongs, that has been last transmittedsuccessfully, may be used, as described in FIG. 2. Also, the terminalmay determine whether a difference between the current CQI that ismeasured at stated intervals and reflects the downlink channel quality,and the CQI used to calculate power headroom of the power headroominformation that has been last reported successfully, exceeds apredetermined threshold indicated in Condition 1.

If it is determined in step 320 that Condition 1 is satisfied, theterminal proceeds to step 325. Otherwise, if Condition 1 is unsatisfied,the terminal returns to step 315 and performs uplink data transmissionand power headroom measurement.

In step 325, the terminal checks whether Condition 2 is satisfied. Thatis, the terminal checks in step 325 whether the sum of uplink datastored at the present time exceeds predetermined Y indicated inCondition 2. If the sum of the stored data exceeds Y, the terminalproceeds to step 330 and otherwise proceeds to step 315. Depending onthe terminal, Y may be set to zero (0). That is, it may be determinedthat Condition 2 is satisfied unless the terminal's buffer is empty.Subsequently, the terminal generates power headroom information andtransmits the power headroom information to the base station accordingto a predetermined procedure in step 330, and then returns to step 315,or ends the operation.

Second Embodiment

In a second embodiment of the present invention, a terminal checks thesatisfaction/non-satisfaction of Condition 1 and Condition 2 immediatelybefore transmitting uplink data instead of constantly checking thesatisfaction/non-satisfaction, so the terminal may transmit the powerheadroom information along with uplink transmission data, withoutrequesting allocation of separate transmission resources despite thegeneration of the power headroom information. Use of the secondembodiment of the present invention may ensure more efficient use oftransmission resources because the terminal does not request separatetransmission resources, for transmission of power headroom information.

Referring to FIG. 4, the terminal recognizes Condition 1 and Condition2, which are power headroom information generation conditions, in step405. Condition 1, as described above, is satisfied when a change in pathloss is greater than or equal to a predetermined threshold when a changein power headroom is greater than or equal to a predeterminedarea-specific threshold, or when a change in CQI is greater than orequal to a predetermined threshold. Condition 2, as described above, issatisfied when the amount of data stored in the terminal is greater thanor equal to a predetermined threshold. Having completed a call setupprocess, the terminal notifies the base station of the amount of itstransmission data by transmitting a BSR according to a predeterminedprocedure in step 410. When a terminal with no transmission data reportsthe generation of new transmission data using the BSR, the terminal maytransmit the power headroom information as well, while transmitting theBSR.

After successfully transmitting the BSR and the power headroominformation in step 410, the terminal monitors a downlink controlchannel in step 413. While monitoring the downlink control channel, theterminal may measure the path loss or downlink channel status ifnecessary. Based on the measured downlink channel status, the terminaldetermines a Channel Quality Information (CQI) value it periodicallytransmits to the base station. While monitoring the downlink controlchannel in step 413, the terminal is allocated uplink transmissionresources by receiving uplink scheduling information in step 415.Thereafter, the terminal determines in step 420 whether Condition 1 issatisfied. The process of determining whether Condition 1 is satisfiedin step 420 is identical to step 320 described in the first embodiment,so a detailed description is omitted here.

If Condition 1 is satisfied in step 420, the terminal proceeds to step425, and if Condition 1 is unsatisfied, the terminal proceeds to step440. In step 425, the terminal checks whether Condition 2 is satisfied.Namely, the terminal determines in step 425 whether the sum of uplinkdata stored at the present time exceeds a predetermined data amountthreshold Y indicated in Condition 2. If the sum of the stored dataexceeds data amount threshold Y, the terminal proceeds to step 430, andotherwise, the terminal proceeds to step 440. The sum of uplink datastored in the terminal in step 425 is a value determined by subtractingthe amount of data to be transmitted using the transmission resourcesallocated in step 415 from the total amount of data at the present time.For example, if the base station instructed in step 415 the terminal totransmit 500-byte data and the terminal has stored data of a total of1000 bytes in step 425, then the terminal compares a value determined bysubtracting 500 bytes from 1000 bytes with the data amount threshold Y.

In step 430, the terminal calculates power headroom using the currentpath loss, and generates power headroom information including thecalculated power headroom. In step 435, the terminal generates uplinkdata with the power headroom information, and then proceeds to step 445.If either Condition 1 or Condition 2 is unsatisfied even though theterminal was allocated the uplink transmission resources in step 415,the terminal generates uplink data according to the common procedure instep 440 and then proceeds to step 445, because the terminal does notgenerate power headroom information. In step 445, the terminal transmitsthe uplink data generated in step 435 using the allocated transmissionresources, and then returns to step 413 to monitor the downlink controlchannel, or ends its operation depending on the terminal's situation.

Third Embodiment

In the second embodiment of the present invention, Condition 2 ischecked before power headroom information is generated. The reason forchecking Condition 2 in the embodiment of the present invention is todetermine the amount of data left in the terminal after data with thepower headroom information was transmitted is greater than or equal to apredetermined threshold. Therefore, more accurate results may beobtained by checking Condition 2 after generating data with the powerheadroom information.

Accordingly, the third embodiment of the present invention provides amethod in which if uplink transmission resources are allocated andCondition 1 is satisfied, the terminal generates data with powerheadroom information and then compares the amount of its remaining datawith data amount threshold Y, to transmit the data with the powerheadroom information as it is, or to transmit new data in which thepower headroom information is replaced by user data.

Referring to FIG. 5, the terminal recognizes Condition 1 and Condition2, which are power headroom information generation conditions, through acall setup process in step 505. Condition 1, as described above, issatisfied, for example, when a change in path loss is greater than orequal to a predetermined threshold. Condition 2, as described above, issatisfied when the amount of data stored in a terminal is greater thanor equal to a predetermined threshold.

Having completed a call setup process, the terminal notifies the basestation of the amount of its transmission data by transmitting a BufferStatus Report (BSR) according to a predetermined procedure in step 510.When the terminal with no transmission data reports the new generationof transmission data using the BSR, the terminal may transmit the powerheadroom information as well, while transmitting the BSR.

After successfully transmitting the BSR and the power headroominformation in step 510, the terminal monitors the downlink controlchannel in step 513. While monitoring the downlink control channel, theterminal may measure the path loss or downlink channel status ifnecessary. Based on the measured downlink channel status, the terminaldetermines a CQI value it periodically transmits to the base station.

While monitoring the downlink control channel, the terminal is allocateduplink transmission resources by receiving uplink scheduling informationin step 515. Thereafter, in step 520, the terminal measures powerheadroom for transmission of uplink data and determines whetherCondition 1 is satisfied, based on the measured power headroom. Theprocess of determining whether Condition 1 is satisfied in step 520 isidentical to step 320 described in the first embodiment, so a detaileddescription is omitted here.

If Condition 1 is satisfied in step 520, the terminal proceeds to step525, and otherwise, the terminal proceeds to step 540. In step 525, theterminal calculates power headroom using the current path loss, andgenerates power headroom information with the calculated power headroom.In step 530, the terminal generates uplink data with the power headroominformation, and then determines in step 535 whether the sum of dataleft in the terminal's buffer is greater than or equal to data amountthreshold Y. If the sum of the remaining data is greater than or equalto data amount threshold Y, the terminal proceeds to step 550, and ifthe sum of the remaining data is less than data amount threshold Y, theterminal proceeds to step 545. Proceeding to step 545 indicates that itis efficient to transmit user data instead of power headroom informationbecause of the low utility of the power headroom information due to thesmall amount of the remaining data. In step 545, the terminal removesthe power headroom information and generates new uplink data with theremaining data. In step 550, the terminal transmits the uplink datagenerated in the previous step using the allocated transmissionresources. The terminal then returns to step 513 to monitor the downlinkcontrol channel, or ends its operation according to the terminal'ssituation. If Condition 1 is unsatisfied in step 520, the terminalgenerates uplink data according to the common procedure in step 540, andthen proceeds to step 550.

Referring to FIG. 6, a terminal according to the present inventionincludes an upper layer device 601, a multiplexer 605, a controller 610,a downlink control channel processor 615, and a transceiver 620.

The controller 610 is notified of Condition 1 and Condition 2 by theupper layer device 601 in charge of call setup. The controller 610controls the transceiver 620 to measure uplink data and necessarycontrol information. In other words, the controller 610 is adapted tomeasure at least one of power headroom, path loss, and downlink channelquality at stated intervals. Also, the controller 610 determines whethereither Condition 1 or Condition 2 is satisfied. If so, the controller610 generates appropriate power headroom information and provides it tothe multiplexer 605. According to the first embodiment, the controller610 generates power headroom information based on power headroommeasured for uplink data transmission during transmission of uplink dataif both of Condition 1 and Condition 2 are satisfied. According to thesecond embodiment, upon receiving a notification indicating theallocation of uplink transmission resources from the control channelprocessor 615, the controller 610 generates power headroom informationif both of Condition 1 and Condition 2 are satisfied. According to thethird embodiment, upon receiving a notification indicating theallocation of uplink transmission resources from the control channelprocessor 615, the controller 610 generates power headroom informationif Condition 1 is satisfied, and then determines whether Condition 2 issatisfied.

The multiplexer 605 multiplexes the uplink data provided from the upperlayer with the power headroom information generated by the controller610. In other words, the multiplexer 605 generates uplink data includingthe power headroom information generated by the controller 610.

The transceiver 620 transmits/receives the uplink data or controlinformation through wireless channels.

The control channel processor 615 monitors the downlink control channel(e.g., a channel carrying allocation information for uplink transmissionresources) the transceiver 620 has received, and if uplink transmissionresources are allocated, the downlink control channel processor 615notifies the controller 610 of the allocated uplink transmissionresources.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting power headroominformation by a terminal in a mobile communication system, the methodcomprising: determining, by the terminal, whether a path loss haschanged more than a threshold when the terminal has an allocated uplinktransmission resource; and if the path loss has changed more than thethreshold, obtaining power headroom information, generating an uplinkdata packet including the power headroom information, and transmittingthe uplink data packet by using the allocated uplink transmissionresource, wherein the power headroom information in Decibels (dB) isobtained based on:Power Headroom=P _(MAX) −P _(REQUIRED), wherein P_(MAX) is a maximumtransmission output of the terminal, and P_(REQUIRED) is a requiredtransmission power, which is obtained based on the path loss andinformation related to a Modulation Coding Scheme (MCS).
 2. The methodof claim 1, wherein generating the uplink data packet includesmultiplexing uplink data provided from an upper layer with the powerheadroom information.
 3. The method of claim 1, wherein the requiredtransmission power is obtained based on:P _(REQUIRED)=10 log n+Po+α×PL+delta_(—) mcs+f(delta_(—) i) wherein Poand α are positive real numbers that are stored in the terminal, or aresignaled by a base station in a call setup process, PL is the path lossmeasured by the terminal, delta_mcs is an arbitrary integer individuallypredetermined for each MCS, and f(delta_i) is a value that the terminalobtains by inputting uplink transmission output control commandsreceived up to present time, to a specific function.
 4. A terminalapparatus for transmitting power headroom information in a mobilecommunication system, the apparatus comprising: a controller fordetermining whether a path loss has changed more than a threshold whenthe terminal has an allocated uplink transmission resource, and, if thepath loss has changed more than the threshold, obtaining power headroominformation; a multiplexer for generating an uplink data packetincluding the power headroom information; and a transceiver fortransmitting the uplink data packet by using the allocated uplinktransmission resource, wherein the power headroom information inDecibels (dB) is obtained based on:Power Headroom=P _(MAX) −P _(REQUIRED), wherein P_(MAX) is a maximumtransmission output of the terminal, and P_(REQUIRED) is a requiredtransmission power, which is obtained based on the path loss andinformation related to a Modulation Coding Scheme (MCS).
 5. The terminalapparatus of claim 4, wherein the multiplexer is configured to generatethe uplink data packet by multiplexing uplink data provided from anupper layer with the power headroom information.
 6. The terminalapparatus of claim 4, wherein the required transmission power isobtained based on:P _(REQUIRED)=10 log n+Po+α×PL+delta_(—) mcs+f(delta_(—) i) wherein Poand α are positive real numbers that are stored in the terminal, or aresignaled by a base station in a call setup process, PL is the path lossmeasured by the terminal, delta_mcs is an arbitrary integer individuallypredetermined for each MCS, and f(delta_i) is a value that the terminalobtains by inputting uplink transmission output control commandsreceived up to now, to a specific function.
 7. A method of receivingpower headroom information by a base station in a mobile communicationsystem, the method comprising: receiving, by the base station, the powerheadroom information; and performing allocation of an uplinktransmission resource to a terminal by referencing the received powerheadroom information, wherein the received power headroom information istransmitted by the terminal by determining, by the terminal, whether apath loss has changed more than a threshold when the terminal has anallocated uplink transmission resource; if the path loss has changedmore than the threshold, obtaining, by the terminal, the power headroominformation; generating, by the terminal, an uplink data packetcomprising the power headroom information; and transmitting, by theterminal, the uplink data packet by using the allocated uplinktransmission resource, wherein the power headroom information inDecibels (dB) is obtained based on:Power Headroom=P _(MAX) −P _(REQUIRED), wherein P_(MAX) is a maximumtransmission output of the terminal, and P_(REQUIRED) is a requiredtransmission power, which is obtained based on the path loss andinformation related to a Modulation Coding Scheme (MCS).
 8. The methodof claim 7, wherein generating the uplink data packet includesmultiplexing uplink data provided from an upper layer with the powerheadroom information.
 9. The method of claim 7, wherein the requiredtransmission power is obtained by the terminal, based on:P _(REQUIRED)=10 log n+Po+α×PL+delta_(—) mcs+f(delta_(—) i) wherein Poand α are positive real numbers that are stored in the terminal, or aresignaled by the base station in a call setup process, PL is the pathloss measured by the terminal, delta_mcs is an arbitrary integerindividually predetermined for each MCS, and f(delta_i) is a value thatthe terminal obtains by inputting uplink transmission output controlcommands received up to now, to a specific function.
 10. A base stationapparatus for receiving power headroom information in a mobilecommunication system, wherein the base station apparatus is configuredfor: receiving the power headroom information; and performing allocationof an uplink transmission resource to a terminal by referencing thereceived power headroom information, wherein the received power headroominformation is transmitted by the terminal by determining, by theterminal, whether a path loss has changed more than a threshold when theterminal has an allocated uplink transmission resource; if the path losshas changed more than the threshold, obtaining, by the terminal, thepower headroom information; generating, by the terminal, an uplink datapacket comprising the power headroom information; and transmitting, bythe terminal, the uplink data packet by using the allocated uplinktransmission resource, wherein the power headroom information inDecibels (dB) is obtained based on:Power Headroom=P _(MAX) −P _(REQUIRED), wherein P_(MAX) is a maximumtransmission output of the terminal, and P_(REQUIRED) is a requiredtransmission power, which is obtained based on the path loss andinformation related to a Modulation Coding Scheme (MCS).
 11. Theapparatus of claim 10, wherein generating the uplink data packetincludes multiplexing uplink data provided from an upper layer with thepower headroom information.
 12. The apparatus of claim 10, wherein therequired transmission power is obtained by the terminal, based on:P _(REQUIRED)=10 log n+Po+α×PL+delta_(—) mcs+f(delta_(—) i) wherein Poand α are positive real numbers that are stored in the terminal, or aresignaled by the base station in a call setup process, PL is the pathloss measured by the terminal, delta_mcs is an arbitrary integerindividually predetermined for each MCS, and f(delta_i) is a value thatthe terminal obtains by inputting uplink transmission output controlcommands received up to now, to a specific function.